Smart mobile devices such as mobile phones have a variety of user input methods for controlling the device, in particular tapping a screen or button or speech recognition. The in-air gesture has long been recognized as a very attractive alternative due to its unique intuitiveness, richness and convenience. However in air gesture recognition technologies which recognize complex gestures, for example based on cameras, require processing of continuous video frames, in addition to the fact that image sensors are generally not low power components. Camera-based solutions may require good illumination to work correctly and may be sensitive to light disturbance.
Moreover, other systems for example optical sensors, near field sensors and capacitive sensors may not recognize complex gestures, whether predetermined or user-defined.